1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a magnetic head for perpendicular magnetic recording that has a main pole and a shield.
2. Description of Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure where a read head having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head includes a main pole that produces a magnetic field in a direction perpendicular to the plane of the recording medium. The main pole includes, for example, a track width defining portion having an end located in a medium facing surface that faces the recording medium, and a wide portion that is connected to the other end of the track width defining portion and is greater in width than the track width defining portion. The track width defining portion has a generally constant width. To achieve higher recording density, it is required that the write head of the perpendicular magnetic recording system be smaller in track width and improved in write characteristics such as overwrite property which is a parameter indicating an overwriting capability.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface mentioned above. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). The slider is designed to slightly fly over the surface of the recording medium by means of an airflow that comes from the air inflow end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air outflow end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In particular, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew mentioned above can cause the phenomenon that signals already written on one or more tracks that are adjacent to a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing (such a phenomenon will hereinafter be referred to as adjacent track erasure). For higher recording densities, it is necessary to prevent adjacent track erasure.
A known technique for preventing adjacent track erasure induced by a skew is to configure the main pole so that its end face located in the medium facing surface decreases in width with increasing proximity to the top surface of the substrate, as disclosed in U.S. Patent Application Publication Nos. US 2004/0150910 A1 and US 2009/0059426 A1, for example. U.S. Patent Application Publication Nos. US 2004/0150910 A1 and US 2009/0059426 A1 also disclose configuring the main pole so that its thickness in the vicinity of the medium facing surface decreases with increasing proximity to the medium facing surface.
In order to prevent skew-induced problems, it is also effective to reduce the thickness of the main pole in the medium facing surface. If the entire main pole is thinned, however, the main pole becomes small in cross-sectional area perpendicular to the direction in which magnetic flux flows. This makes it difficult for the main pole to direct much magnetic flux to the medium facing surface, thus leading to degradation of overwrite property.
Configuring the main pole so that its thickness in the vicinity of the medium facing surface decreases with increasing proximity to the medium facing surface as disclosed in U.S. Patent Application Publication Nos. US 2004/0150910 A1 and US 2009/0059426 A1 makes it possible to reduce the thickness of the main pole in the medium facing surface and increase the thickness of a portion of the main pole away from the medium facing surface to allow the main pole to direct much magnetic flux to the medium facing surface.
In order to prevent adjacent track erasure induced by a skew and provide higher recording densities, it is effective to provide a write shield that has an end face located in the medium facing surface at a position forward of the end face of the main pole in the direction of travel of the recording medium, as disclosed in U.S. Patent Application Publication No. US 2009/0059426 A1.
In a magnetic head having the write shield, there are typically provided one or more return path sections for connecting the write shield to part of the main pole away from the medium facing surface. The write shield and the one or more return path sections function to capture a magnetic flux that is produced from the end face of the main pole and spreads in directions other than the direction perpendicular to the plane of the recording medium, and to thereby prevent the magnetic flux from reaching the recording medium. The write shield and the one or more return path sections also function to allow a magnetic flux that has been produced from the end face of the main pole and has magnetized the recording medium to flow back to the main pole.
The position of an end of a record bit to be recorded on the recording medium depends on the position of an end of the end face of the main pole located in the medium facing surface, the end being located forward in the direction of travel of the recording medium. In order to define the position of the end of the record bit accurately, it is therefore important that the write shield have an end face that is located in the medium facing surface at a position forward of the end face of the main pole in the direction of travel of the recording medium and that this end face of the write shield capture a magnetic flux that is produced from the end face of the main pole and spreads in directions other than the direction perpendicular to the plane of the recording medium. The magnetic head having the write shield is capable of preventing adjacent track erasure and provides a further improved recording density.
As described above, configuring the main pole so that its thickness in the vicinity of the medium facing surface decreases with increasing proximity to the medium facing surface makes it possible to reduce the thickness of the main pole in the medium facing surface and increase the thickness of a portion of the main pole away from the medium facing surface to allow the main pole to direct much magnetic flux to the medium facing surface. Nevertheless, there may be cases where the portion of the main pole away from the medium facing surface has an insufficient thickness.
To cope with this, it is also effective to connect a yoke layer to the portion of the main pole away from the medium facing surface to increase the total thickness of the main pole and the yoke layer while reducing the thickness of the main pole in the medium facing surface, as disclosed in U.S. Patent Application Publication No. US 2009/0059426 A1.
Now, a problem with the magnetic head having the write shield and the yoke layer will be described. To make full use of the effect of the yoke layer mentioned above, a front end face of the yoke layer facing toward the medium facing surface is preferably brought as close to the medium facing surface as possible. However, this causes a decrease in the distance between the front end face of the yoke layer and the write shield, thereby causing an increase in magnetic flux leakage from the yoke layer to the write shield to cause degradation of write characteristics such as the overwrite property. Typically, a corner having an angle of 90° is formed between the front end face of the yoke layer and each of top and bottom surfaces of the yoke layer, and magnetic flux tends to leak from inside to outside the yoke layer at the corner, in particular. A decrease in the distance between the front end face of the yoke layer and the write shield causes an increase in magnetic flux leakage from the corner of the yoke layer to the write shield.
It has thus been difficult for conventional magnetic heads having the write shield and the yoke layer to prevent the skew-induced problems and provide improved write characteristics.